Production of a semiconductor device involves a step of forming an electroconductive film on the surface of a wafer to form a wiring layer by photolithography, etching etc., a step of forming an interlaminar insulating film on the wiring layer, etc., and an uneven surface made of an electroconductive material such as metal and an insulating material is generated on the surface of a wafer by these steps. In recent years, processing for fine wiring and multilayer wiring is advancing for the purpose of higher integration of semiconductor integrated circuits, and accordingly techniques of planarizing an uneven surface of a wafer have become important.
As the method of planarizing an uneven surface of a wafer, a CMP method is generally used. CMP is a technique wherein while the surface of a wafer to be polished is pressed against a polishing surface of a polishing pad, the surface of the wafer is polished with an abrasive in the form of slurry having abrasive grains dispersed therein (hereinafter, referred to as slurry). As shown in FIG. 1, a polishing apparatus used generally in CMP is provided for example with a polishing platen 2 for supporting a polishing pad 1, a supporting stand (polishing head) 5 for supporting a polished material (wafer) 4, a backing material for uniformly pressurizing a wafer, and a mechanism of feeding an abrasive. The polishing pad 1 is fitted with the polishing platen 2 for example via a double-sided tape. The polishing platen 2 and the supporting stand 5 are provided with rotating shafts 6 and 7 respectively and are arranged such that the polishing pad 1 and the polished material 4, both of which are supported by them, are opposed to each other. The supporting stand 5 is provided with a pressurizing mechanism for pushing the polished material 4 against the polishing pad 1.
Conventionally, such polishing pads are produced by batch methods such as (1) a method including pouring a resin material into a mold to form a resin block and slicing the resin block with a slicer; and (2) a method including pouring a resin material into a mold and pressing the resin material into a thin sheet form.
A method for continuously producing a polyurethane-polyurea polishing sheet material is proposed in order to prevent variations in hardness, cell size or the like attributed to batch production method (Patent Literature 1). Specifically, the proposed method includes mixing a raw material for polyurethane, a fine powder having a diameter of 300 μm or less, and an organic foaming agent, discharging the mixture to the space between a pair of caterpillar belts to cast it, then carrying out the polymerization of the mixture with heating means, and separating the generated sheet-shaped product from the surface belt so that a polishing sheet material is obtained. When a pair of caterpillar belts is used, however, there is a problem in which the resulting polyurethane foam tends to have flat cells and therefore has low polishing performance.
There is also proposed a method for continuously producing an elastic sheet that includes supplying a raw material for a polyurethane foam onto a base film being continuously supplied and subjecting the raw material to a reaction and curing, while the thickness of the raw material for the polyurethane foam is controlled using two rollers and a surface protection film (Patent Literature 2). However, this method also has the same problem as described above.
There is also disclosed a method for continuously producing a polishing pad having an undercoat layer and a polishing layer, which is for the purpose of reducing the difference between polishing pads produced in different batches (Patent Literature 3). In the method of Patent Literature 3, however, it is difficult to adjust the thickness of a fluid-phase polymer composition supplied onto the undercoat layer, so that a polishing layer with high thickness accuracy cannot be produced.    Patent Literature 1: JP-A 2004-169038    Patent Literature 2: JP-A 2005-227392    Patent Literature 3: JP-A 2003-516872